In the milling of rock and cementitious materials, it is often required to remove large amounts of material, including hard mineral deposits, fairly rapidly. Machines have been proposed for this purpose in order to increase productivity and reduce labor costs over manual methods. Many such proposed tools have used oscillation in combination with other motions, such as in a rotating mining tool, to cut rock with less energy than otherwise would be required. Attempts to produce a machine using these concepts have met with limited success, however, due to the destructive nature of oscillation forces.
Another situation in which oscillation has been used to enhance the machining of rock is in drilling operations, such as core drilling through rock formations. Devices proposed for this purpose have used a pair of counter-rotating, eccentrically-weighted cylinders to create vibrational forces in the direction of a drill string. Such mechanisms remain free to move in directions other than the direction of the drill string, however, and therefore result in destructive oscillations, as well. Thus, it is desirable to provide a vibratory milling machine capable of rapidly removing rock or cemetitious material and yet having a long useful life.